GENERAL ZOOLOGY 



Zygotes of P^ 

 generation 



Gametes of P 



Q y ] Zygotes of Fj 

 generation 



Daughters heterozygous Sons normal for color vision 



but normal for color vision 



Zygotes of Fj 



.V I Gametes of F^ 



• y ) Zygotes of F2 



Zygotes of F2 



Gametes of F2 



Zygotes of F3 



Normal but 



heterozygous 



daughters 



Color-blind 

 daughters 



Color-blind 

 sons 



Fig. 6.22. Inheritance of color blindness in man. The gene for a defective retina is located 

 in the X-chromosome, which explains the crisscross transmission from a color-blind man to half 

 the sons of his daughters. Color-blind daughters may occur if a woman heterozygous for color 

 vision marries a color-blind man, as shown in the third cross. The symbol for a female is $; 

 S is the symbol for a male. An X-chromosome carrying a gene for normal color vision is 

 indicated by o; • indicates an X-chromosome carrying a gene for color blindness; y is the 

 Y-chromosome of the male. 



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